Unfortunately they sound terrible arco so now I have to play cello when I play in my wife's orchestra. :(
[edit] it occurs to me that you're talking about electric bass... in which case nylon strings would be a bit strange ;) sorry about that.
Not at all, there are nylon wrapped strings for electric now too! [1]
[1] http://www.daddario.com/DADProductFamily.Page?ActiveID=3768&...
I've always wanted to play heavy strings, so I also explored tuning down. Imagine my surprise seeing what Dimebag Darrell was tuning to for "Floods" on 'Great Southern Trendkill' - C# F# B E G# C. I had trouble getting intonation that worked well for me, so I went ahead and got a Les Paul style Baritone. Definitely a workout, and the opposite of going lighter, but I really dig the tone it puts out. Worth the hand cramps to practice on the 27" scale.
I'd definitely be more inclined to trust in his musical intuition than his scientific aptitude though.